Sound reproducing apparatus



H. BELAR SOUND REPRODUCING APPARATUS March 28, 1939.

Filed Dec. 2, 1935 3 Sheets-Sheet l ll 'IvIvvv I I N VEN TOR. 16 588597 EELAI? ATTORNE Y.

March 28, 1939.

H. BELAR 2,152,173

soum) REPRODUCING APPARATUS Filed Dec. 2, 1935 3 Sheets-Sheet 2 24 /5 24' 15 g L 4M 1) 20 j (L 2L 29x 20 3 0 AVIVQA'A A A fl l l l T-j A An I "Y" INVENTOR.

ATTORNEY.

March 28, 1939.:

H. BELAR 2,152,173

SOUND REPRODUCING APPARATUS Filed Dec. 2, 1935 34 X I A \MAMNV?NVW 1 3.9 a

I N VEN TOR. HERBERT 8614/? ATTORNEY.

s Sheets- Sheet s Patented Mar. 28, 1939 SOUND REPRODUCING APPARATUS Herbert Belar, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application December 2, 1935, Serial No. 52,458

10 Claims.

This invention relates to the reproduction of soundfrom photographic or like records, and has for its principal object the provision of an improved apparatus and method of operation for 5 reproducing sound from different types of records such as those having the positive and negative half cycles recorded on a single track, those having-the alternate half cycles recorded on separate track or those of other types.

lif- It is well known that the type of sound record produced by a photographic recorder is dependent on the form of light beam varied or modulated inaccordance with the sound to be recorded. Thus in one type of single track recording, a

15 triangularly-shaped light beam is vibrated transversely of a light slit. Similarly in one type of push-pull recording, a pair of triangularly-shaped beams having their vertices pointed in opposite directions are likewise vibrated transversely of a 20 light slit to record the positive and negative half cycles on separate tracks.

It is desirable to be able to reproduce these various types of records by means of a single apparatus which is readily adjusted toreproduce 25 sound from the type of record which happens to be available. In accordance with the present invention, this result is achieved by the provision of means which are readily operated to adapt the connections of the amplifier and photoelectric 30 tube for reproducing sound either from a single track sound record or from a plural track sound record.

Another important consideration in the reproduction of push-pull sound records and in the 35 circuit readjustments made when different types of records are to be reproduced is the balancing of the outputs of the different photoelectric tubes. Such balancing may be effected by means of potentiometers or by varying the anode potentials to control the sensitivity of the tubes. Further objects of the invention are the provision of improved methods of balancing the outputs of the photoelectric tubes and theprovision of an improved apparatus whereby these methods may be 45 put into practice. p

The invention will be better understood from the following description when considered in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

50 Referring to the drawings,

Fig. 1 is a diagrammatic illustration of a sound reproducer operable to reproduce sound either from a single track record or from a record of the p -p p 55 Fig, 2 is awiring diagramof a sound reproducer wherein the balance between the phototube outputs is maintained by means of independent polarizing voltage supply potentiometers,

Fig. 3 illustrates the use of the balancing system of Fig. 2 in connection with a transformer having only one primary winding,

' Fig. 4 illustrates a slightly modified balancing system,

Figs. 5 and 6 illustrate a balancing system suitable for use in connection with photoelectric tubes of the vacuum type which do not vary in sensitivity with change in the polarizing voltage, and

Figs, 7 and 8 illustrate balancing circuits which do not necessarily involve the use of a transformer.

The reproducing apparatus of Fig. 1 includes a source H] from which light passes through an optical unit I l to a record strip lZwhich bears near one of its edges either (1) a. single track sound record or (2) a push-pull sound record such, for example, as that disclosed by Glenn L. Dimmick application Serial No. 610,302 filed May 9, 1932 (D-6'738), and assignedto the same assignee as the present application. This push-pull record disclosed by the aforesaid application may assume various forms but preferably comprises a pair of tracks which (1) are spaced from one another and (2) respectively bear records of the positive and negative half cycles of the recorded sound wave. During the reproduction of the push-pull record light modulated by one of these tracks passes through lenses l3 and I4 to a cathode 15 of a, photoelectric tube [6 and light modulated by the other of these tracks similarly passes through lenses i3 and I! to a cathode 18 of the tube it. During reproduction of the single track record light modulated by both half cycles passes tothe two cathodes.

The cathode I5 is connected to one end terminal of a resistor I9 which is shunted across the primary winding-20 of a transformer 2| provided with a secondary winding 22. The cathode i8 is connected to one terminal of a switch 23 and the anode is connected through a polarizing battery 25 to another terminal of the switch 23.

When the apparatus is to be operated for re producing a push-pull record, the switch 23 is moved to its upper closed position thus connecting the cathode l8 to the upper end of the resistor i9 and connecting the anode 24 through the battery 25 to the adjustable mid-terminal 26 of the resistor I9. When the apparatus is to be operated for reproducing a single track record, the switch 23 is moved to its lower closed position thus connecting the cathodes l5 and 18 to the lower end terminal of the resistor 19 and connecting the .55

light responsive element is intended to indicate a photoelectric cathode-anode. unit irrespective of whether such unit involve the use of separate anodes or of separate receptacles.

In order to balance the outputs from the different light responsive elements and compensate for diiferences in sensitivity and the like each element may be provided with an independently adjustable source of polarizing voltage. With gas filled tubes, the sensitivity of each tube or element may be adjusted to balance the outputs. This adjustment may be made either by introducing hum through the exciter lamp ID or by the use of a suitable test film and adjusting the polarizing voltages until the outputsneutralize each other. I

Fig. 2 illustrates a reproducing apparatus wherein (1) a compensating unit including potentiometers 21 and 28 and a condenser 29 is provided for adjusting the potential of a light responsive element I 8-24 and (2) a compensating unit including resistors and 3| and a condenser 32 is provided for adjusting the potential of the light responsive element I5-24'. In both cases, the polarizing potential is determined by the position of the adjustable mid-terminal of the potentiometer 21 or 30.

The means for changing from single to double track operation and vice versa is similar to that of Fig. 1. Thus 1) when the switch 23 is moved to its right hand closed position, the primary windings 23 and 20 of the transformer 21 are connected to produce in the secondary winding 22 currents which are opposed and (2) when the switch 23 is moved to .its left hand closed position, secondary currents of the same polarity are induced inthe winding 22. It will be apparent that balancing of the outputs may be efiected by the adjustment of only one of the mid-terminals of the potentiometers 21 and 30.

Fig. 3 illustrates a reproducer apparatus wherein the transformer 2| is not provided with separate primary windings as the arrangement of Fig. 2 but is provided with a center or mid= terminal. The operation of this modification is similar to that of Fig. 2. Thus movement of the switch 23 to its lower closed position connectsthe apparatus for double track or push-pull operation and movement of the switch to its upper closed position connects the apparatus for single track operation.

The reproducer of Fig. 4 is similar to that of Fig. 3 except that the series resistors 28 and 3| are replaced by a single resistor 33 provided with an adjustable center terminal to which the positive lead of the polarizing voltage source is connected for simultaneously adjusting the voltages of the two light responsive elements.

The reproducers of Figs. 3 and 4 are more particularly adapted for use in connection with light responsive elements of the gas filled type. In the case of vacuum cells where the sensitivity does not change with the polarizing voltage, other means for balancing the outputs may be employed. Such means are illustrated in Figs. 1, 5 and 6.

The arrangements of Figs. 5 and 6 differ from that of Fig. 1 only with respect to the connections of the resistor I9. The arrangement of Fig. 6 has the advantage that the loading of the transformer is not appreciably changed by large impedance of the light responsive elements. In the case of Fig. 1, the impedance of the potentiometer l9 should control the output. This requires that the'refiected impedance of the transformer be higher than if no center terminal is employed. V

In cases where it is desirable to avoid the use of a transformer, the potentiometer may be coupled directly to the amplifier. In such cases, the balance between the outputs may be eflected either by means of a volume control potentiometer or by'controlling the polarizing voltage as indicated in connection with the previous figures.

Fig. 7 illustrates an arrangement wherein the outputs of the two light responsive elements are supplied through condensers 34 and 35 and a resistor 36 to the input circuits of a pushepull The function ofthe switch 23 in as in the previous amplifier 31. this arrangement is the same arrangements.

Fig. '8 illustrates the application of the apparatus to a single tube amplifier 38. In this arrangement the switch 23 is utilized (1) to connect the light responsive element [3-24 in a bridge circuit 3940l524 for push-pull track operation and (2) to connect the element Iii-24 in parallel with the element I5-24' for single track operation. Thus movement of the switch 23 to its'lower closed position connects the element I 8-24 between the outside end terminals of the resistors 39 and 40, the resultant current of the resistor is dependent on the relation between the outputs of the two elements and the potential applied through the condenser 34 and the resistor 36 to the input circuit of the amplifier 38 is determined by magnitude and polarity of the resultant current which may flow in one or the other direction as indicated by arrows.

I claim:

1. A sound reproducer including a plurality of light responsive elements, an amplifier circuit, and means operable to connect said elements to said circuit either in push-pull or parallel relation with one another.

2. A sound reproducer including a. plurality of light responsive elements, an. amplifier circuit, means operable to connect said elements to said circuit either in push-pull or parallel relation with one another, and means for balancing the outputs of said elements.

3. A sound reproducer including a plurality of light responsive elements, an amplifier circuit, means operable to connect said elements to said circuit either in push-pull or parallel relation with one another, and means comprising adjustable sources of polarizing voltage for balancing the outputs of said elements.

4. A sound reproducer including a plurality of light responsive elements, an amplifier circuit, means operable'to connect said elements to said circuit either in push-pull or parallel relation with one another, and means comprising independently adjustable sources of polarizing voltage for balancing the outputs of said elements.

5. The combination of an impedance device including three sections adjustably connected together at their inner ends and each provided with an exterior terminal, an amplifier provided with an input circuit connected between one pair of said exterior terminals, a pair of light responsive devices, means for connecting one of said devices between another pair of said exterior terminals, and means for connecting the other of said devices between either of said pairs of exterior terminals.

6. The combination of an impedance device, an amplifier provided with an input circuit connected to said device, a pair of light responsive elements, and means for connecting said elements to said device either in parallel with or in opposition to one another.

7. Apparatus for the reproduction of sound records from films of the asymmetric" and normal types, comprising two photo-sensitive elements each responsive to one lateral zone of a film, switching means for alternatively connecting said elements in parallel for the reproduction of normal films and in push-pull relationship for the reproduction of "asymmetric films.

8. Apparatus for the reproduction of sound records from films, comprising two photo-sensi tive elements each responsive to one lateral zone of a film, an output transformer coupled with said elements, and a change-over switch connected with a transformer winding.

9. Apparatus for .the reproduction of sound records from films, comprising two photo-sensitive elements each responsive to one lateral zone of a film, a common 'output circuit for said elements, and a switch for cutting out of the circuit one of said elements.

10. In an arrangement for the reproduction of sound records from films, a photoelectric cell having two cathodes each responsive to a difierent lateral zone of a film, an impedance having one terminal connected with one and the other with the other cathode, a switch in the connection leading to one cathode, and a contact for said switch connected with the other cathode.

HERBERT BELAR. 

